I. Field of the Invention
This invention relates to a sonic and/or ultrasonic generator for the mechanical breakage of high consistency bubbles constituting industrial foams. It can therefore be assigned to the industrial instrumentation sector, with applications in the field of industrial fermentation processes.
II. Description of the Related Art
The problems associated with an excess of foam in industrial processes affect a large number of sectors such as food, pharmaceuticals, the chemical sector, etc. In some of these sectors, and more specifically in those based on fermentation processes, an excess of foam constitutes one of the most serious problems. In particular, an excess of foam leads to a reduction in the capacity of tanks, deficiencies in the process and reactions, spillages and losses of product, difficulties in dosing the container and filling, harmful effects on machinery and equipment, and so on.
Foams are produced in reactors, fermenters, mixers, packaging machines, etc. There exist very different types of foam, and it can be stated that the degree of difficulty for elimination of the foam depends on the foam's characteristics. The methods most commonly used for defoaming are: chemical, mechanical and thermal. Chemical methods are the most effective but they have the problem of contaminating the product. Mechanical procedures such as mobile blades, jets of air or water, etc., are good for thick foams but have little effect on fine foam. Thermal methods consist of heating and cooling the foam, and are expensive and difficult to apply.
The capacity of high intensity sonic and/or ultrasonic waves for producing breakage of foams has been known for decades [see R. M. G. Boucher and A. L. Weiner “Foam control by acoustic and aerodynamic means” British Chemical Engineering vol. 8, 1963, pp. 808-812], though its application has been very limited. This situation can be basically attributed to the lack of adequate macrosonic generators. The acoustic power generators initially used were of the aerodynamic type (sirens, acoustic whistles) which, apart from possessing low efficiency [see H. Hollfelder, Improving the efficiency of stem-jet whistles, Ultrasonics 5, 250-51, 1967)], give rise to a series of collateral problems such as air currents, heating, etc., which hinder their application.
The problem of industrial defoaming has acquired greater importance in recent years on account of growing restrictions on the use of chemical defoamers (the method most used so far), particularly in sectors such as food and pharmaceuticals. This means that the application of macrosonic waves (high intensity sound or ultrasound) is again being considered as a possible means of non-contaminating industrial defoaming. Nevertheless, the most recent precedents on “macrosonic defoaming” resort to the application of sound and/or ultrasound through the liquid [see N. Ueno, Y. Nishi, T. Sakurai, “Method of ultrasonic waves degassing and device using the same”, U.S. Pat. No. 6,106,590, 2000. H. K. Ratcliff, “Rotating sonic energy wave”, U.S. Pat. No. 3,761,732, 1972, Apparatus for defoaming liquids, U.S. Pat. No. 1,075,100, 1966, F. Shuhei, “Ultrasonic defoaming tank”, European Patent EP10020253, 1998., J. A. Gallego-Juárez, “High Power Ultrasound” in Wiley Encyclopedia of Electrical and Electronics Engineering, vol. 9, pp. 49-59, 1999], which in reality implies not the breakage of the foam but instead the degassification of the liquid which is a different process. In fact, in “macrosonic degassification” the wave is generated in the liquid mass and the dissolved gas or gas in the form of small bubbles inside it groups together, forming large size bubbles which gradually increase with oscillation, rising towards the surface where they finally escape from the liquid. This is a phenomenon widely referred to in the literature as “rectified diffusion” [see T. G. Leighton “the acoustic bubble”, Academic Press. London 1994] and [L. Bjorno, “High-power Ultrasonics: Theory and Applications” Proc. of the 13th International Congress on Acoustics, Belgrade 1989, pp. 77-89].
“Macrosonic defoaming” is a process of destroying bubbles forming a foam by means of cyclically positive and negative pressure amplitudes generated by high intensity sonic and/or ultrasonic waves impinging on the foam from the air. The mechanisms for breakage of bubbles induced by macrosonic radiation are basically resonances of the bubbles, radiation pressure, friction between bubbles, acoustic currents and atomization of the film which forms the bubble [L. Bjorno, “High-power Ultrasonics: Theory and Applications” Proc. of the 13th International Congress on Acoustics, Belgrade 1989, pp. 77-89].